Evaluation of protectivity and immunogenicity of alum precipitated autoclaved Leishmania major vaccine mixed with Mycobacterium vaccae in the murine model of leishmaniasis

ABSTRACT

Leishmaniases represent a group of diseases caused by protozoan parasite of the genus Leishmania. Control strategies are not always effective, it seems that the sole control measure is to search for an effective vaccine. The objective of this study was evaluation of the rate of protection and immune response induction in Balb/c mice immunized with alum precipitated autoclaved Leishmania major [Alum-ALM] vaccine mixed with M. vaccae. Eleven groups of female 8-10 week old Balb/c mice were immunized subcutaneously [SC] three times, 21 days apart, with different doses of Alum-ALM mixed with different doses of either M. vaccae or BCG. The immunized animals and control group were challenged with 1 x 10 [6] L. major. Development and progression of leishmania infection were assessed by footpad swelling measurement at the site of challenge and parasite burden in lymph nodes. The immune responses of vaccinated animals were evaluated in vivo by leishmanin skin test [LST] and in vitro by measurement of cytokine [IFN-lamda and IL-4] levels in mononuclear cell culture] supernatants and titration of serum anti-leishmania antibodies [IgG and its sub-classes]. Footpad thickness measurment after challenge with live L. major showed no significant difference between immunized groups and control group. However, there were some prominent exceptional cases in the parasite burden titration in groups 1, 4, 6, and 8. Immunization with low dose of Alum-ALM mixed with M. vaccae or BCG induced IFN-lamda production, and diminished IL-4 level [in vitro], and caused a stronger LST response in a group that received BCG as an adjuvant. Mice that were immunized with high doses of Alum-ALM mixed with high doses of M. vaccae showed an increase in footpad thickness at the site of challenge and higher levels of IL-4 and IgGl. It seems that immunization of mice with a low dose of Alum-ALM mixed with M. vaccae as an adjuvant might induce a Thl type response. M.vaccae mixed with low dose of Alum-ALM has an inhibitory influence on the parasite burden in the infected tissues of mice. Also, BCG mixed with different doses of Alum-ALM induces a Thl immune response in Balb/c mice. Apparently, there is no significant difference in adjuvancity of BCG and M. vaccae. High dose of Alum-ALM mixed with high dose of M. vaccae induces a Th2 response